The present invention relates to a map display apparatus that three-dimensionally displays a two-dimensional map (plane map) as a bird""s eye view map achieved by converting the two dimensional map into a bird""s eye view display format, whereby ground levels and roads are displayed either depressed or elevated in correspondence to their altitudes, and a map database device and a recording medium to be employed in such a map display apparatus.
Map display apparatuses for vehicles that display a roadmap through the so-called bird""s eye view method, whereby the area on the roadmap in the vicinity of the current position of the vehicle is displayed larger than the area on the roadmap in the distance on a display apparatus, are known in the prior art (for instance, see Japanese Laid-Open Patent Publication No. Heisei 2-244188). In the apparatus disclosed in the publication mentioned above, the viewpoint is set behind the current position of the vehicle and the view obtained by looking down from this viewpoint in the advancing direction of the vehicle is displayed on the screen of the display apparatus. Since the map information in regard to the vicinity of the current position can be displayed in an enlargement and a wide range of view from the current position to a distant position can be displayed by implementing map display through such bird""s eye view method (hereafter a map displayed through the bird""s eye view method is referred to as a bird""s eye view map to be differentiated from a two-dimensional map which is displayed in two dimensions), the state of the connection between roadmap areas can be visually ascertained with a greater degree of ease. In addition, roadmap display that gives the driver the feeling that he is actually looking down on the area of the roadmap is achieved.
While three-dimensional display of roads and the like displayed in such a bird""s eye view map is achieved by adding height data to positional coordinate data of the individual element points on roads, the volume of data will become too large, and as a result, three-dimensional display is implemented only for specific structures such as bridges and interchanges in a map display apparatus for vehicles. However, it is difficult to achieve three-dimensional display of all the roads, bridges and interchanges through this method due to the high memory capacity requirements, which will result in an increase in production costs and it is even more difficult to display the ground levels with depressions and elevations in correspondence to their altitudes.
An object of the present invention is to provide a map database device with which the volume of the data indicating altitudes can be reduced when three-dimensionally displaying the ground levels and roads in a bird""s eye view map in correspondence to their altitudes, a recording medium in which the relevant map data are recorded, and a map display apparatus that utilizes the data with a high degree of efficiency.
In order to achieve the object described above, the map database device according to the present invention is employed to display a bird""s eye view map achieved by converting a two-dimensional map into a display format of a bird""s eye view method. And the map data base device comprises: a height data portion in which height data respectively corresponding to altitudes of a plurality of areas into which the two-dimensional map is divided are respectively stored in correspondence to the areas.
This makes it possible to reduce the volume of the data indicating altitudes required for three-dimensionally displaying ground levels and roads in a bird""s eye view map based upon their altitudes.
An alternative map database device is employed to display a bird""s eye view map achieved by converting a two-dimensional map into a display format adopting the bird""s eye view method. The map database device comprises: a height data portion in which height data respectively corresponding to altitudes of a plurality of areas into which the two-dimensional map is divided are respectively stored in correspondence to the areas; and a road data portion in which a road extending within the two-dimensional map is expressed with a plurality of element points and positional coordinates of each of the element points in the two-dimensional map are stored.
This, in addition to achieving an advantage similar to that described above, makes it possible to incorporate altitude data with the road data.
A map display apparatus according to the present invention displays a bird""s eye view map achieved by converting a two-dimensional map into a display format adopting the bird""s eye view method. And the map display apparatus comprises: a database device that includes at least a height data portion in which height data respectively corresponding to altitudes of a plurality of areas into which the two-dimensional map is divided are respectively stored in correspondence to the areas, and a road data portion in which a road extending within the two-dimensional map is expressed with a plurality of element points and positional coordinates of each of the element points in the two-dimensional map are stored; and a calculation means for performing calculation to determine in which of the areas the element point read out from the road data portion is located, reading out height data corresponding to the area ascertained through the calculation from the height data portion to use as height data for the element point, and calculating coordinate values of the element point on the bird""s eye view map to be displayed on a monitor screen based upon positional coordinates read out from the road data portion and the height data obtained through calculation.
This makes it possible to three-dimensionally display roads in the bird""s eye view map based upon their altitude data while reducing the volume of the data indicating the altitudes.
An alternative map display apparatus displays a bird""s eye view map by converting a two-dimensional map into a display format adopting the bird""s eye view method. And the map display apparatus comprises: a height data portion in which height data respectively corresponding to altitudes of a plurality of areas into which the two-dimensional map is divided are respectively stored in correspondence to the areas; a calculation means for calculating coordinate values on the bird""s eye view map to be displayed on a monitor screen for a point in each of the areas based upon positional coordinates and height data of the point; and a gradation means for achieving gradation display of areas enclosed by the points on the monitor screen in correspondence to heights of the individual points.
This achieves simplification in the calculation for the gradation display when displaying the ground levels in a bird""s eye view map in gradations based upon their altitude data while keeping down the volume of data required.
An alternative map display apparatus displays a bird""s eye view map achieved by converting a two-dimensional map into a display format adopting the bird""s eye view method. And the map display apparatus comprises: a map database device that includes a height data portion in which height data respectively corresponding to altitudes of a plurality of areas into which the two-dimensional map is divided are respectively stored in correspondence to the areas, and a tunnel data portion in which a tunnel within the two-dimensional map is expressed with a plurality of element points and positional coordinates of each of the element points in the two-dimensional map are stored; and a calculation means for performing calculation to determine which of the areas element points corresponding to an entrance and an exit among the element points read out from the tunnel data portion are located in, reading out height data corresponding to the areas determined through the calculation from the height data portion to use as height data of the entrance and the exit, interpolating other element points with the height data of the entrance and the exit to create height data therefor, and calculating coordinate values of the element points on the bird""s eye view map to be displayed on a monitor screen based upon positional coordinates read out from the tunnel data portion and height data obtained through calculation.
With this, since the height in the middle section of the tunnel is calculated through interpolation using the heights at the entrance and the exit in order to display the section between the tunnel entrance and the tunnel exit as a dotted line or the like to make it appear as if it was present underground, the tunnel can be displayed in a natural manner without the middle section of the tunnel present on the ground level while reducing the volume of data representing altitudes.
An alternative map display apparatus displays a bird""s eye view map by converting a two-dimensional map into a display format adopting the bird""s eye view method. And the map display apparatus comprises: a height data portion in which height data respectively corresponding to altitudes of a plurality of areas into which the two-dimensional map is divided are respectively stored in correspondence to the areas; a calculation means for calculating coordinate values on the bird""s eye view map to be displayed on a monitor screen for a point in each of the areas based upon positional coordinates and height data of the point; and a gradation means for calculating a difference between a minimum height and a maximum height among a plurality of areas enclosed by the points within the monitor screen, respectively assigning m sets of color data among color data determined in advance with fixed gradation pitch to m color palettes in a predetermined order when the difference is equal to or less than a specific value, calculating a variable gradation pitch by dividing the difference by m if the difference exceeds the specific value to assign m sets among the color data provided in the predetermined order to the m color palettes with the variable gradation pitch, in order to achieve gradation display of each of areas enclosed by the points on the monitor screen in correspondence to heights of the individual points.
With this, it becomes possible to implement gradation display in color by efficiently utilizing a limited number of color palettes while minimizing the volume of data representing altitudes.
A recording medium according to the present invention which can be read by a computer, records: map data that has a height data portion in which height data respectively corresponding to altitudes of a plurality of areas into which a two-dimensional map is divided are respectively stored in correspondence to the areas for displaying a bird""s eye view map by converting the two-dimensional map into a display format of bird""s eye view method.
This makes it possible to provide map data with a reduced volume of data representing altitude stored in the recording medium when three-dimensionally displaying ground levels and roads in a bird""s eye view map based upon their altitudes.
An alternative map display apparatus displays a bird""s eye view map by converting a two-dimensional map into a display format adopting the bird""s eye view method. The map display apparatus comprises: map data that include two-dimensional map data and height data; and a three-dimensional bird""s eye view map display means for three-dimensionally displaying the bird""s eye view map on a display screen based upon the map data taking the height data into consideration. And: the map data comprise detailed map data at a large scaling factor and wide range map data at a scaling factor smaller than the detailed data; the display screen is divided into, at least, a first display area and a second display area adjacent to the first display area, the first display area being set at a side closer to a viewpoint in a bird""s eye view method, and the second display area being set on a side further away from the viewpoint; and the three-dimensional bird""s eye view map display means displays a three-dimensional bird""s eye view map in the first display area based upon the detailed map data, displays a three-dimensional bird""s eye view map in the second display area based upon the wide range map data, sets a hypothetical line of sight that extends from the viewpoint to pass through a point corresponding to a boundary of the first area and the second area on the display screen, and determines ranges, over which the detailed map data and the wide range map data are to be used, in reference to a point at which the line of sight intersects a line corresponding to a ground level calculated by taking the height data into consideration.
With this, since the position at which the display screen is split is changed in consideration of the height of the ground level, the image does not become disconnected in the vicinity of boundaries of the detailed information area and the wide range information area when expressing depressions and elevations in the ground level.